1. Technical Field
This disclosure relates to a recordable optical recording medium for use in recording information by means of laser beam irradiation and specifically relates to a recordable optical recording medium, which may be hereinafter referred to as “optical disc”, capable of reducing the track pitch width to thereby obtain high-density recording, and the present invention also relates to a recording and reproducing method using the optical recording medium.
2. Description of the Related Art
It has been known that a margin is provided to track pitch of a recordable optical disc in order to prevent cross-write, cross-erase, and cross-talk events, which are caused from thermal interference between adjacent tracks. For example, when the wavelength of a laser beam for use is 405 nm, and the numerical aperture NA of an object lens of the optical system is 0.85, the track pitch of the optical disc is typically set to 320 nm or more.
For such optical discs in the prior art, there are many proposals on preventing cross-write, and cross-erase events. For example, with respect to structural characteristics of optical discs, the following optical discs have been proposed. Namely, an optical disc in which a recording area formed on a substrate is separated for each track, and a material having a smaller thermal conductivity than that of a recording material constituting the recording area is laid in between the tracks (see Japanese Patent Application Laid-Open (JP-A) No. 2000-276770); an optical disc in which a recording layer is provided only on guide grooves formed on the substrate, and no recording layer is laid in between the guide grooves (see Japanese Patent Application Laid-Open (JP-A) No. 2001-236689); an optical disc in which at both sides of boundary portions that land flat parts formed on the substrate make contact with inclined surfaces of boundaries between each of the lands and each grooves, convex portions each of which is higher than the flat part of land is formed consecutively and longitudinally to the land parts (see Japanese Patent Application Laid-Open (JP-A) No. 2004-39106); and an optical disc in which laminar structured recording layers are formed on adjoining land parts and groove parts on a quartz substrate in a discontinuous manner (see Japanese Patent Application Laid-Open (JP-A) No. 2001-266405), and the like.
However, it is extremely difficult to completely prevent cross-write and cross-erase events even with any of the optical disc structures in the prior art, and it is impossible to drastically reduce the track pitch width. The applicant proposed an optical recording medium in which a linear-shaped conductor in a direction parallel to the track direction of a laser beam is provided on the substrate (see Japanese Patent Application Laid-Open (JP-A) No. 2003-228880). However, in the proposal, an optical recording medium capable of providing completely satisfactory performance has not been obtained yet, and further improvements and developments are still required.